Test 1: CHE 140 Study Guide: Matter, Temperature, Energy, Units, Density, and Conversions

Matter

Definition and Classification

Matter is anything that has mass and occupies space. A chemical is a substance that has the same composition and properties wherever it is found.

• Pure Substances:

  • Elements: Substances made of only one type of atom. Example: O2 (oxygen gas).

  • Compounds: Substances composed of two or more different elements chemically bonded together. Example: H2O (water).

• Mixtures:

  • Heterogeneous Mixtures: Composition is not uniform throughout. Example: salad, oil and water.

  • Homogeneous Mixtures: Also called solutions; composition is uniform throughout. Example: salt water, air.

Visual Identification: Be able to interpret diagrams showing elements (identical atoms), compounds (identical molecules of two or more atoms), and mixtures (more than one type of particle, either mixed uniformly or not).

Chemical and Physical Properties and Changes

• Chemical Properties: Describe a substance's ability to undergo changes that transform it into different substances. Example: flammability, reactivity.

• Chemical Changes: Changes that result in the formation of new substances. Example: rusting of iron.

• Physical Properties: Characteristics that can be observed without changing the substance's identity. Example: melting point, color, density.

• Physical Changes: Changes that do not alter the identity of a substance. Example: melting ice, dissolving sugar in water.

Temperature

Understanding Temperature and Scales

• Temperature is a measure of the average kinetic energy of the particles in a substance.

• Know the freezing and boiling points for all three temperature scales:

  • Celsius (°C): Freezing = 0°C, Boiling = 100°C

  • Fahrenheit (°F): Freezing = 32°F, Boiling = 212°F

  • Kelvin (K): Freezing = 273 K, Boiling = 373 K

• Understand the extent of the ranges for all 3 temperature scales.

Temperature Conversion Formulas

• To convert between Celsius and Kelvin: $K = ^\circ C + 273$

• To convert between Celsius and Fahrenheit: $^\circ F = (^\circ C \times \frac{9}{5}) + 32$

• To convert between Fahrenheit and Celsius: $^\circ C = (^\circ F - 32) \times \frac{5}{9}$

Note: When reporting temperature, match the decimal place of your answer to the tenths place of the input value.

Energy

Kinetic and Potential Energy

• Kinetic Energy: Energy due to motion. Example: a moving car.

• Potential Energy: Stored energy due to position or composition. Example: a stretched spring.

Heat and Units of Energy

• Heat is the energy associated with the motion of particles.

• Common units:

  • Joule (J): SI unit of energy.

  • Calorie (cal): Amount of energy needed to raise the temperature of 1 gram of water by 1°C.

Calorie and Joule Relationship

• 1 calorie (cal) = 4.184 joules (J)

• Be able to convert between calories and joules.

Food Energy Calculations

• Know how to calculate kcal from nutrition content and grams of carbs, fats, or protein.

• kcal/gram for fats, carbs, and protein will be provided on the test.

Units and Measurements

SI System and Measurements

• Know the base units for the metric (SI) system:

Quantity	SI Unit
Mass	kilogram (kg)
Volume	liter (L)
Length	meter (m)
Time	second (s)

• Know how to use scientific notation and significant figures.

• Be able to use significant figures in multiplication, division, addition, and subtraction, and round answers appropriately.

• Understand what exact numbers are and how to identify them.

Density

Definition and Calculation

• Density is mass per unit volume.

• Formula: $\text{Density} = \frac{\text{mass}}{\text{volume}}$

• Units: g/mL, g/cm3

• Density can be used to identify substances and predict whether an object will float or sink in water.

Volume Calculations

• If you have density and mass, you can find volume: $\text{Volume} = \frac{\text{mass}}{\text{density}}$

• If you have density and volume, you can find mass: $\text{Mass} = \text{Density} \times \text{Volume}$

• Volume can be obtained by multiplying length × width × height for regular solids.

Specific Gravity

• Specific gravity is the density of a substance divided by the density of water.

• Density of water is 1.00 g/mL.

• Specific gravity is unitless.

Unit Conversions

Metric Prefixes and Conversion Factors

• Know your metric prefixes (e.g., kilo-, centi-, milli-).

• Conversion factors are used to convert between units.

• When converting between metric values, conversion factors are exact numbers and do not affect significant figures.

U.S. to Metric and U.S. to U.S. Conversions

Conversion	Value
1 gallon	4 quarts
1 mile	5280 feet
1 inch	2.54 cm (exact)
1 L	1.06 quarts
1 kg	2.20 lbs
1 km	0.621 miles

• When converting between U.S. and metric, only the measured number has significant figures (except for 1 in = 2.54 cm, which is exact).

• Understand how percentages and statements like 65 km/h can be used as conversion factors.